Beam steering is useful in many areas of science and technology, including the manufacture of laser printers and compact disc players, optical communications, integrated optics and laser radar.
The traditional way to steer laser beams has been through the use of external optics. Mechanical beam steering systems, however, are limited in their speed and mechanical stability. These limitations have led to the development of techniques to integrate the laser source and the steering system on the same chip. The resulting monolithic beam steering systems are compact, fast and mechanically stable.
Two main parameters are used to describe the performance of a beam steering system: the total steering angle, that is, the maximum angle that can be spanned by the laser beam intensity peak, and the number of separable spots in the far field, referred to as resolvable spots.
The original monolithic beam steering techniques have focused on altering the phase front of laser modes inside the laser cavity in order to change the position of the far-field intensity peak. These techniques have included twin-stripe lasers, differentially pumped single waveguide lasers, and Offset Gain and Index Guided (OGIG) lasers. One of the disadvantages of these techniques is that the beam exhibits large modal distortion with power and current variations. In addition, the total steering angle is less than 30.degree., with five or fewer resolvable spots. As a result of the modal distortion, the far field intensity distributions are not usually single symmetric Gaussian modes. Therefore a significant fraction of the optical power is unusable.
Another system that has been used for multiple spot addressing is the parallel laser array. Parallel laser arrays are suited for the addressing of points spanning rectangular surfaces. Parallel laser arrays, however, can not be used effectively for beam steering, since the total steering angle for such systems is usually very small. Moreover, the total number of laser stripes in parallel arrays is limited by the light-collecting optics and by thermal and electrical crosstalk between the lasers.